Ion Tiriac, the former manager and coach of Boris Becker, says he is not sure how effective his former pupil will be as a coach to Novak Djokovic.

"I don't know if Boris is a good coach," the billionaire former player told German newspaper Bil am Sonntag, saying he did now know enough about the arrangement. "I don't even know if he is a coach... Maybe he is learning how to be a coach."

Tiriac did say that Becker should focus on the mental and tactical aspects of the game with Djokovic. "If Boris tries to improve the technique and shots of Djokovic, he is the wrong man for the job," said Tiriac. "You cannot teach a world-class player like Djokovic more in this respect.

Players like Nadal and Djokovic, he added, "need someone who know more about the game than them and can lead them," pointing to how Ivan Lendl has "mentally" helped Murray.

Last week in Dubai, Djokovic repeated that Becker had been recruited largely for his big-match experience.

"We're not significantly changing anything," said Djokovic. "The biggest thing he can contribute is the mental approach. That's one of the reasons Boris is here, because of the big matches and the Grand Slams. I felt I dropped two or three titles in the last two years I could have won."

Tiriac is not the only former Becker guide to express misgivings about the six-time Grand Slam champion's appointment as Djokovic's coach. Nikki Pilic, who served as Germany 's Davis Cup captain when Becker played for the team and was also one of Djokovic's early coaches, told Focus magazine earlier this year, "There is no doubt that Boris must change his lifestyle completely."

"He needs strict discipline and a certain modesty," said Pilic of Becker, who released an autobiography last year with several attention-grabbing revelations about his former wife and a one-time fiancee. "It won't be easy for him but he has no choice."

Roger Federer and Lleyton Hewitt also expressed surprise shortly after the new pairing was announced.